SOLDERLESS WRAPPED CONNECTIONS PART II 569 



Fig. 13 — Photoelastic picture of a terminal when the outside wire diameter 

 approaches the terminal diameter. 



stresses indicated are in the order of 50 to 60 per cent of the winding 

 stresses in agreement with the photoelastic experiments. Ratios of 5 to 

 1 on the length- width ratio were also tried with substantially the same 

 result. To determine how much dissymmetry is necessary to lock in the 

 bending stresses, a ratio of 1.25 to 1 of the length to width was tried with 

 the result shown by the lower curve of Fig. 12. The stripping force for 

 this ratio is about half that for the larger ratios. The conclusion is that 

 the stripping force decreases as the symmetry increases but that a small 

 deviation from circular symmetry is sufficient to lock in the bending 

 stress. However, for the more satisfactory connections, other factors 

 such as adequate intimate gas tight contact areas indicate that the 

 required dissjTnmetry involves abrupt surface changes in the nature of 

 edges having appreciable penetrating power with respect to the wire. 

 Therefore, while a terminal like that of Fig. 12 may have the ability to 

 lock in the bending stresses, it may not, for other reasons, be the better 

 terminal to use. 



All of the photoelastic and other types of stress measurements were 

 made for terminals that have a large stiffness in torsion and as seen by 

 the photoelastic pictures, the stresses are nearly plane stresses, i.e., they 

 are all tensions, compressions or shears in a plane perpendicular to the 

 axis of the connection. If, however, the torsional stiffness becomes low, 

 another type of deformation can take place, namely, a twist of the whole 

 terminal due to the torque put on by the helical form of the winding. 

 Fig. 13 shows a photoelastic picture of the strain in the terminal when 



